The appearance of harmful “algal” blooms (HABs) in recent years in the western basin of Lake Erie has focused attention on the threat to public health posed by these organisms. Of concern in Lake Erie are the so-called ‘blue-green algae’. These organisms are not actually algae, but rather are cyanobacteria. Most important among the cyanobacteria are Microcystis aeruginosa and related species. These organisms produce potent cyanotoxins which collectively are referred to as microcystins. Phosphorus availability is thought to be the primary factor in cyanobacterial growth, but the “bloom” phenomenon appears to be due to a more complex set of factors. Biotic and abiotic factors that may play a role include dreissenid mussel abundance, the concentration and speciation of nitrogen, and temperature. Also, it has been documented by the Pennsylvania Department of Environmental Protection that Presque Isle Bay (PIB) has become more eutrophic in recent years, possibly leading to algal blooms and an overall degradation of water quality. Since the waters of Presque Isle Bay are of value and interest to the community and the state, the protection of the aquatic ecosystem of PIB and the protection of the health of persons using the Bay for recreation and fishing is a worthy goal. The objectives of this project are to 1) conduct a thorough literature search of published and unpublished but locally available water quality and biological measurements of PIB waters and tributaries for relevant data; 2) determine the frequency of occurrence of prior HABs in PIB and Lake Erie; 3) to apply knowledge of the aquatic ecology of PIB along with collected water quality, abiotic, and biotic information to create an aquatic ecosystem computer model of PIB capable of predicting HABs; and 4) use the predictive model to examine the benefit of various ‘best management practices’ that could be used in the watershed and the Bay to determine their impact on the likelihood of HAB occurrence.